In wireless communication systems, mobile units or devices operate on batteries. To conserve power, these mobile units go inactive/idle/dormant on the wireless channels after a short period of non-usage. For data services this period is usually 30 to 60 seconds. Therefore, in push-to-talk calls using the wireless data services, both the originating and terminating mobile units must be transitioned to an active state (actually using wireless resources) as part of the call setup prior to enabling the push-to-talk communication. Once a mobile unit is in the active state, a wireless channel has been established and the mobile unit is able to transmit and/or receive data. As known in the art, push-to-talk call applications include transmission of voice and associated signaling data, but advances in packet data networks extend push-to-talk call applications to include images, streaming video, text messaging, stored audio files, and other multi-media.
For typical push-to-talk call applications, the time required for transitioning an originating mobile unit from a dormant/idle state to the active state can be more than 3 seconds in current implementations. An equal or greater amount of time is required to transition the terminating mobile unit from the dormant to active state, including additional time to actually page the mobile device, as is known in the art. These times do not include transmission time over the air or call processing time required by the dispatch controllers. As a result, for the push-to-talk function total delay times experienced by the originating mobile unit may be 8 seconds or greater.
With long call setup times, the advantages of the push-to-talk service as an instant communications method is diminished. In fact, with call setup times of 8 seconds or longer, the service may be non-viable in the marketplace. For instance, users may prefer to simply use cellular, rather than holding down their PTT button.
A similar problem exists for group calls in the push-to-talk mode. Call setup times may be even longer since there are multiple terminating mobile units to connect to the originating mobile unit. Although some of the processing time for each of the terminating or target mobile units may overlap, the total call setup time is even greater than the individual-to-individual call. Therefore, group calls pose an even greater problem for the push-to-talk function in a packet data network.
As previously mentioned, paging the mobile units involves significant delay. The radio access network (RAN) may need to first locate the MS using a page/page response exchange, which typically takes 400+ ms. Also, when a base transceiver station (BTS) attempts to page a mobile, it must wait for the appropriate paging channel (PCH) slot to send a message to the MS operating in slotted mode. This is known as the “slot cycle delay,” which can be up to 5.12 seconds for a Slot Cycle Index (SCI) value of 2. In addition, page messages can be dropped during periods of high PCH loading. Typically, the recovery mechanism is for the source of the message to resend after a lengthy timeout. Moreover, some of these paging-related delays impact other instant messaging services in addition to PTT, such as short message service (SMS).
Accordingly, it would be highly desirable to have a method and apparatus for substantially decreasing paging-related delays in wireless systems.